1. Field of the Invention
This invention generally relates to a clutch cover assembly provided with a wear compensating mechanism. More specifically, the present invention relates to a wear compensating mechanism, which can operate when wear occurs on a friction member, and thereby moves a fulcrum of a pressing member toward the friction member in accordance with an amount of wear.
2. Background Information
A clutch cover assembly of a clutch device is attached to a flywheel of an engine. The clutch cover assembly operates to press a friction facing of a clutch disk assembly against the flywheel by an elastic force of a diaphragm spring or the like for transmitting a drive force of an engine to a transmission. In this clutch device, when the friction facing wears to a predetermined extent or wears beyond the predetermined extent, the friction facing cannot be used any longer. If use continues after such wear, the position of the diaphragm spring of the clutch cover assembly changes so that the pressing load disadvantageously changes. Therefore, the clutch disk assembly must be replaced with a new clutch disk assembly when the wear occurs to the predetermined extent or more. It has been desired to increase the use time of the clutch disk or the replacement cycle, and therefore the lifetime of the clutch.
For increasing the lifetime of the clutch, it is important to increase an effective service thickness of the friction facing in the clutch disk assembly. In view of this increased thickness, the friction facing is fixed to a cushioning plate without using a rivet or the like according to one of several known methods of attachment.
In the clutch cover assembly, it is necessary to return the attitude (orientation) of a spring such as a diaphragm spring to the initial attitude (orientation) when the friction facing is worn. Therefore, such a wear compensating mechanism is used that determines an amount of wear of the friction facing. The wear compensating mechanism can move a fulcrum (a fulcrum ring on the pressure plate side or a fulcrum mechanism on the clutch cover side) of the spring such as a diaphragm spring in accordance with the determined amount of wear. Thereby, the attitude (orientation) of the diaphragm spring or the like can be kept constant or maintained in an initial attitude (orientation) independently of the wear of the friction facing. Therefore, the friction facing of the clutch disk assembly can be used to the maximum extent.
In a clutch cover assembly disclosed in Japanese Laid-Open Patent Publication No. 8-170652, a pressing member for applying a pressing force to a pressure plate is formed of a spring and a lever member. The wear compensating mechanism is a mechanism for moving a fulcrum mechanism on the clutch cover side toward the friction facing in accordance with the amount of wear of the friction facing. This wear compensating mechanism is primarily formed of a support member, a biasing mechanism, and a friction detecting mechanism. The support member supports a fulcrum of a lever member on the clutch cover side. The biasing mechanism biases the support member toward the friction member. The friction detecting mechanism detects an amount of friction member wear and allows movement of the pressure plate toward the clutch cover in accordance with the amount of wear.
The biasing mechanism is formed of two ring members having several inclined surfaces, which are in complementary contact with each other, to form a wedge mechanism, and a spring for biasing the ring member on the clutch cover side in the rotating direction. The spring and wedge mechanism act to move the other ring member and a support member toward the friction member.
The friction detecting mechanism is formed of a cylindrical member which is axially movably and frictionally engaged with an aperture in the clutch cover, and a bolt which extends from the pressure plate. The bolt has a head in contact with a side of the cylindrical member remote from the friction member. An axial space corresponding to a release stroke of the pressure plate is maintained between the pressure plate and the cylindrical member. The pressure plate is always biased away from the friction member by a plurality of strap plates. When the biasing force of the diaphragm spring is released and therefore the clutch enters the clutch released state, the pressure plate moves away from the friction member, and comes into contact with a friction member side of the cylindrical member.
When the friction member wears, the pressure plate moves toward the flywheel. Furthermore, the pressure plate moves a bushing relative to the clutch cover by a distance corresponding to the amount of wear of the friction member. As a result, the axial distance between the pressure plate and the cylindrical member is the same as before the wearing of the friction member. When the clutch releasing operation is then performed, the cylindrical member stops the axial movement of the pressure plate. The position where the pressure plate stops is shifted by the amount of wear toward the friction member side from the position before wearing. Therefore, the axial space corresponding to the amount of wear of the friction member is formed between the pressure plate and the lever member. As a result, the biasing mechanism can move the support member in the axial direction, and the lever member comes into contact with the pressure plate when it moves a distance corresponding to the amount of wear.
According to the wear compensating mechanism in the foregoing conventional clutch cover assembly, the amount of wear is detected from the axial space between the pressure plate and the cylindrical member engaged with the clutch cover. The movement and stopping of the support member are performed between the support member and the pressure plate. According to this structure, the pressure plate is moved toward the friction member due to, e.g., vibrations applied thereto in the clutch releasing operation. An excessively large space is then formed between the pressure plate and the support member so that the support member may move a distance larger than the predetermined distance toward the pressure plate. When such over-adjusting occurs, the position of the spring applying a biasing force to the pressure plate changes from the initial state so that the pressing load cannot be constant.
In view of the above, there exists a need for a clutch cover assembly having a wear compensating mechanism which overcomes the above mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.